Corona discharge apparatus with a rotatable roller electrode having a multiplicity of corona discharge spikes mounted thereon



y 1966 K. M. OLIPHANT CORONA DISCHARGE APPARATUS WITH A ROTATABLE ROLLER ELECTRODE HAVING A MULTIPLICITY OF CORONA DISCHARGE SPIKES MOUNTED THEREON 2 Sheets-Sheet l Filed Jan. 18, 1965 INVENTOR. KEITH MERED/TH OL/PHANT y 31, 1966 K. M. OLIPHANT 3,254,215

CORONA DISCHARGE APPARATUS WITH A ROTATABLE ROLLER ELECTRODE HAVING A MULTIPLICITY OF CORONA DISCHARGE SPIKES MOUNTED THEREON Filed Jan. 18, 1965 2 Sheets-Sheet 2 4 I2 I 7 r ITH 5 INVENTOR. KEITH MEREDITH OL/PHA/VT United States Patent 3,254,215 CORONA DISCHARGE APPARATUS WITH A ROTATABLE ROLLER ELECTRODE HAVING A MULTIPLICITY OF CORONA DISCHARGE SPIKES MOUNTED THEREON Keith Meredith Oliphant, Longwood, South Australia,

Australia, assignor' to Research Laboratories of Australia Limited, now Research Laboratories of Australia Pty. Limited, North Adelaide, South Australia, Australia Filed Jan. 18, 1965, Ser. No. 426,170 6 Claims. '(Cl. 250-495) This invention relates to a charging machine for xerographic-and electr-ophotographic materials. This application is a continuation-in-part of application Serial No. 92,257, filed February 28, 1961, now abandoned.

In xerography and electrophotography it is necessary to charge a photoconductor material prior to the formation thereon of a light image, such charging usually being effected by a corona producing device fed from a suitable high voltage source.

One of the problems in charging such materials is that of ensuring that a uniform charge is ap lied over the complete area without the formation of a non-uniform charge pattern introduced by irregularities in the charging device.

A further problem is to so construct the machine that simple manipulation will be possible without operator danger from the high voltages used.

Other problems are associated with the movement of the materials through the charging Zone due to the field introducing electrostatic force-s on the pho'toconductive paper or the like which tends to cause such paper to adhere to parts of the machine.

It is the object of this invention to provide an improved machine which will be capable of uniformly charging paper or other xerographic or electrophotographic materials and will do so in a simple manner without risk to the operator.

According to this invention the improved charging machine for xerographic materials comprises a base, con veyor means supported on said base to receive on it the materials to be charged, means to drive the said conveyor means to carry said material through the machine, an electrode consisting of a spiked roller extending across the said conveyor means on the side of its materialcarrying surfaces but spaced therefrom, said spikes forming a multiplicity of corona discharge elements projecting outwardly from the said roller in staggered rows and in electrical contact with said roller, insulating bearing means on the said base supporting the said spiked roller electrode, means to rotate said spiked roller electrode at a speed such that there is differential movement between the ends of the spikes and the material fed through the machine on the conveyor means, a base electrode associated with the said conveyor means disposed beneath the material passing through the machine adjacent the said spiked roller electrode, and means to supply a direct current potential between the said spiked roller electrode and the said base electrode to induce a corona charging field between the said electrodes.

A plurality of spiked rollers may be used.

The conveyor means preferably comprise a relatively conducting belt, and a base electrode is then disposed beneath the .belt immediately below the surface which carries the paper through the machine and, of course in close proximity to the spiked roller or rollers.

By utilising conveyor means which move the material through the charging zone and by arranging the speed of forward movement of the conveyor means in relation to the spikes in such a way that there is a differential Patented May 31, 1966 speed between them and :by staggering the spikes in the rows, it will be realised that as the material to be charged is moved beneath the spiked roller, the spikes will, as it were, scan the material by sweeping across the material so that the corona discharge between the spikes and the electrode beneath the material will be constantly changed insofar as the position of origin of the corona is concerned, this having a side to side sweeping action as well as a general movement of the corona over the whole of the area covered by the electrodes and resulting in a very greatly improved uniformity of charge.

To enable the invention to be fully appreciated an embodiment will now be described with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of the machine showing same with the cover removed,

FIG. 2 is a side elevation of the machine at the drive end showing the case in section,

FIG. 3 is an enlarged section of the electrodes and belt showing their relative positions, showing a sheet of paper passing on to the belt,

FIG. 4 is a section on line 4-4 of FIG. 3, and

FIG. 5 shows the electrical circuit of the machine.

The base 1 of the machine comprises a floor 2, sides 3 and a top 4 and carries within it the driving motor 5 and the charging unit 6, the charging unit being arranged to produce a voltage between the points 7 of the charging electrodes 8 and the base electrodes 9 suflicient to energise the photoconductor coating on the medium which is fed through the machine.

Normally approximately 15,000 volts would be required with a gap between the electrodes 7 and 9 of approximately one inch.

The roller electrodes 8, of which there are two, are supported on trunnions 10 carried in bearings 11 in plates 12 formed of insulating material. Plates 12 in turn are supported from brackets 13 by bolts and wingnuts 15, the end plates 12 having slots 16 to allow the end plates 12 and thus the electrodes 8 to beraised and lowered in relation to base electrodes 9 for the purpose of adjusting the distance between the roller electrodes 8 and the paper being charged.

The roller electrodes 8 are driven by means of a belt 18 passing around pulleys 19 on the trunnions 10, the belt 18 passing also around a pulley 20 of the shaft 21 projecting from a gearbox 22 forming part of the motor 5.

A tensioning device for the belt 18 comprises an idler pulley 24 revolvable on a stem axially slidable within a support 26 on the top 4 and provided with a lock-screw 27.

To move the paper through the charging zone beneath the roller electrodes 8, a conveyor belt 30 is provided which passes respectively around rollers 31 and 32 having shafts 33 and 34 thereon, the shafts being carried in bearing members 37 projecting upwardly from the top 4.

The shaft 34 carries on it a sprocket 38 engaged by a chain 39 which in turn engages a sprocket on the shaft 21 whichis driven by the motor 5.

The roller 31 has associated with it a floating feed roller 41 which has its ends engaged in slots 42 in the bearing members 37, this roller serving to hold down the paper on to the belt as it is first fed into the machine, after which the paper is held down on to the belt by the electrostatic field through which it moves, the field tending to urge the paper downwardly onto the belt and therefore ensuring that an adequate feed results. The floating feed roller 41 has an insulating covering 43 of rubber or plastic to avoid bleeding away any charge which may exist on the paper as it is fed through the machine, such as when making two passes.

As the roller electrodes 8 have a high voltage on them during operation, a cover 45 fits over the base 1, the

cover having a transparent top 46 so that the operation of the machine may be watched if desired. The cover is provided with an inlet slot 47 at the feed end of the conveyor belt and an outlet slot 48 at the discharge end of the conveyor belt through which the paper enters the charging Zone and subsequently leaves it.

At the inlet slot 47 is provided a table 50 which is disposed at approximately the level of the upper surface of the conveyor belt 30 but has a slightly down-turned lip 51 so that paper placed on the table 50 and pushed forward will engage the conveyor belt 30 and will then be conveyed through the machine, the paper being pressed on to the belt by the aforesaid roller 41.

At the outlet slot 48 is disposed a table 55 supported on brackets 57 which are slidable in bearing members 58 and 59 and provided with adjusting screws 60 and 61 so that by manipulating the screw 60 the table can be raised and lowered and by manipulating the screw 61 the forward position of the table can be varied.

The table 55 is formed of an insulating material to enable the charged sheet to pass across this table without adhering to same.

Both the inlet table 50 and the outlet table 55 are provided with hook-shaped members 56 which engage over the lower edges of the slots 47 and 48 respectively to hold the tables removably in position. 4

The roller electrodes 8 are formed as shown more particularly in FIGS. 3 and 4 of the drawings and comprise a metal member 60 reduced at each end to form the trunnions 10 which are housed in the bearings 11, the bearing 11 at the one end engaging a metal terminal 63 to which the high voltage lead 64 is applied.

The bearings 10 are carried in the end plates 12, which are formed of insulating material, and are held in place by nuts 65 on the bearings.

The conveyor belt 30 as stated earlier, passes around the rollers 31 and 32 but adjacent to each of the roller electrodes, runs over the lower electrodes 9 which are in the form of rollers, trunnions 66 on the rollers 9 engaging bearings 67 in the brackets 13 projecting upwardly from the top 4.

The spikes 7 of the roller electrodes 8 are driven into apertures in an insulating sleeve 71 placed around the outside of the metal member 60 to contact same to ensure that a corona discharge will take place only from the external points of the spikes 7.

The spikes 7 are arranged in a staggered array, as shown in FIG. 1, to increase the effective coverage of the photoconductor surface and assure a uniform surface charge. Uniformity in the surface charge is also enhanced substantially by the fact that rollers 8 rotate in a direction such that the spikes 7 effectively traverse the photoconductor in a direction opposite that in which the conductor is fed through the machine. Thus, despite relatively rapid movement of the photoconductor through the machine, each incremental area thereof is repeatedly scanned by a plurality of the spike electrodes 7 that are axially displaced along the rollers 8.

The bearing member 37, carrying the roller 31, is carried on a pivot 73 and is angularly adjustable by a set screw 74 to allow the belt 30 to be tensioned.

As shown more particularly in FIG. the device for generating the corona discharge on the roller electrodes 8 comprises a transformer 75 in circuit with switch 76 and indicator lamp 77, the transformer stepping up the voltage to the required value and this high voltagebeing passed through a condenser 78 and applied to the roller electrodes 8 therefrom, a rectifier 79 being used to give the polarity required for charging.

The other side of the transformer 75 and rectifier 79 is connected to earth and to the base electrode 9.

The motor 5 which drives the various mechanisms is also shown in the circuit diagram, and its controlling switch is desiganted 80 while an indicator ilght associated therewith is designated 81.

A safety switch 82 is shown in series with the switches 76 and 80, thepurpose of this being to prevent switching on of the mechanism when the cover 45 is removed, the position of the switch 82 being shown in FIG. 1, the cover 45 depressing the movable member of the switch 82 when it is positioned to close the switch and thus place the switches 76 and 89 into a condition where when they are operated the respective units controlled by them will be provided with power.

From the foregoing it will be realised that a simple and effective charging unit is provided into which the material to be charged is fed from a table 50 through a slot 47 on .to a conveyor belt 30, the paper or the like being pressed down on to the conveyor belt by the roller 41 and being then moved by the belt through the two charging localities between the roller electrodes 8 and the base electrodes 9.

The conveyor belt 30 is driven forward at the required rate through the chain 35 while the roller electrodes 8 are revolved by means of the belt 18 while having the necessary current applied thereto to produce a corona discharge from the points of the spikes 7.

The paper or the like is held on to the conveyor belt 30 by gravity and also by electrostatic attraction which exists between the paper and the like while it is being charged and the belt 30. After traversing the machine, the paper or the like leaves the machine through the slot 48 and is discharged on to the table 55 from which the charged paper may be collected.

It is to be noted that the table 55 is disposed so that its one edge is just in contact with the belt 30 a little below its upper level so that as the paper or the like reaches this locality the edge will be guided on to the table'and will be prevented from passing around the roller through attraction between it and the belt.

As previously stated the table '55 is made of an insulating material to prevent the charged sheet from adhering to this table.

While it is possible to achieve a reasonable degree of uniformity of surface charge when the rotating spiked electrode is driven at a circumferential speed somewhere near to the lineal speed of the paper being charged it is obvious that for the purpose of attaining the maximum effects of this invention there should be a substantial difference in speed between the movement of the paper and the movement of the ends of the spikes which may be obtained by for instance the method shown in the drawings where the spikes move contra-wise to the paper and therefore the staggered rows of spikes at all times scan the paper from different points, thereby continually changing the corona position and ensuring that by the sweeping action there will be a most uniform coverage, it having been found for instance that very satisfactory results are obtained by passing a paper heneath the rotating spiked electrode at a speed of 1 to 5 inches per second while the rotating electrode revolves at a speed of to 250 revolutions per minute, but it is to be realised that this high differential speed is not always necessary and the invention is not to be limited to same.

What I claim is:

1. An improved charging machine for xerographic, electrophotographic, and like electrostatic charge image members comprising:

a base;

conveyor means, supported on said base, for receiving an image member to be charged;

means to drive said conveyor means to carry an image member through the machine along a given path;

a roller electrode, extending across one side of said conveyor means in spaced relation to an image member moving through the machine with the axis of said roller electrode extending transversely to said path, said roller electrode having a multiplicity of electrically conductive spikes forming a multiplicity spikes and the image member as the image member is fed through the machine past the roller electrode by said conveyor means;

a base electrode disposed on the opposite side of said electrophotographic, and like electrostatic charge image members comprising:

a base;

conveyor means, supported on said base, for receiving an image member to be charged;

means to drive said conveyor mean-s to carry an image member through the machine along a given path;

a roller electrode, extending across one side of said conveyor means in spaced relation to an image member moving through the machine with the axis of said roller electrode extending transversely to said path, said roller electrode comprising an inner electrically conductive roller, an electrically insulatting sleeve covering said conductive roller, and a multiplicity of electrically conductive spikes forming a multiplicity of corona discharge elements projecting outwardly, from said inner conductive roller through said insulating sleeve for a substantial distance, in staggered rows, said spikes all having their inner ends electrically connected to said inner conductive roller;

means for rotating said spiked roller electrode at a speed and in a direction such that there is a substantial differential in speed and direction of movement between the ends of the spikes and the image member as the image member is fed through the machine past the roller electrode by said conveyor means;

a base electrode disposed on the opposite side of said conveyor means from said roller electrode and facing the opposite side of the image member from said roller electrode;

and means to apply a unidirectional electrical potential between said roller electrode and said base electrode to cause a corona discharge between said spikes and said base electrode to charge the image member.

3. An improved charging machine for xerographic,

electrophotographic, and like electrostatic charge image members comprising:

a base;

a conveyor belt, supported on said base, for receiving an image member to be charged;

means to drive said conveyor belt to carry an image member through the machine along a given path;

a spiked roller electrode, extending across one side of said conveyor belt in spaced relation to an imagespikes and the image member as the image member is fed through the machine past the roller electrode upon said conveyor belt;

a base electrode comprising an electrically conductive roller disposed on and engaging the oppositeside of said conveyor belt from said spiked roller electrode;

and means to apply a unidirectional electrical potential between said spiked roller electrode and said base roller electrode to cause a corona discharge between said spikes and said base roller electrode to charge the image member.

4. An improved charging machine for xerographic,

electrophotographic, and like electrostatic charge image members comprising:

a base;

a conveyor belt, extending over said base, for receiving an image member to be charged;

rollers carried in bearings mounted in said base and supporting said conveyor belt;

means to drive one of said rollers to move said belt and an image member through the machine along a given path;

a plurality of spiked roller electrodes, each extending across the top of said conveyor belt in spaced relation to an image member moving through the machine on saidbelt with the axis of said roller electrode extending transversely to said path, said roller electrodes each having a multiplicity of electrically conductive spikes forming a multiplicity of corona discharge elements projecting outwardly from said roller electrodes in staggered rows, all of said spikes of each such roller electrode being electrically connected to each other;

means for rotating said spiked roller electrodes at a speed and in a direction to cause a substantial differential in movement between the ends of the spikes and the image member such that said spikes repeatedly scan the upper surface of the image member as the image member is fed through the machine past the roller electrodes on said conveyor belt;

a corresponding plurality of base roller electrodes disposed below and engaging the lower side of said conveyor belt, one base roller electrode being aligned with each spiked roller electrode;

and means to apply a unidirectional electrical potential between each of said spiked roller electrodes and the aligned one of said base roller electrodes to cause a corona discharge between said electrodes to charge the image member.

5. An improved charging machine for xerographic,

electrophotographic, and like electrostatic charge image members comprising:

a base;

a conveyor belt, supported on said base, for receiving an image member to be charged;

means, including a drive roller, to drive said conveyor belt to carry an image member through the machine along a given path;

a spiked roller electrode, extending across one side of said conveyor means in spaced relation to an image member moving through the machine with the axis of said roller electrode extending transversely to said path, said spiked roller electrode comprising an inner electrically conductive roller, an electrically insulating sleeve covering said conductive roller, and a multiplicity of electrically conductive spikes forming a multiplicity of corona discharge elements projecting outwardly, from said inner conductive roller through said insulating sleeve, in staggered rows, said spikes all having their inner ends electrically connected to said inner conductive roller;

means for rotating said spiked roller electrode at a speed and in a direction such that there is a substantial differential in speed between the ends of the spikes and the image member as the image member a base electrode comprising an electrically conductive roller disposed on the opposite side of said conveyor roller in staggered rows and all electrically connected to each other,

means for rotating said spiked roller electrode in a direction such that said spikes scan the image member belt from said spiked roller electrode; in a direction opposite the direction of movement and means to apply a unidirectional electrical potential of the image member as the image member is fed between said spiked roller electrode and said base through the machine by said conveyor means; roller electrode to cause a corona discharge between a base electrode disposed on the opposite side of said said spikes and said base roller electrode to charge conveyor means from said roller electrode and facing the image member. 10 the opposite side of the image member from said 6. An improved charging machine for xerographic, spiked roller electrode; electrophotogra-phic, and like electrostatic charge image and means to apply a unidirectional electrical potential members comprising: between said spiked roller electrode and said base a b electrode to cause a corona discharge between said conveyor means, supported on said base, for receiving sPikfis and Said base elsctrode to charge the image an image member to be charged; member; V means to drive said conveyor means to carry an image References Cited by the Examiner member through the machine in a given d1rect1on; a spiked roller electrode, extending across one side of UNITED STATES PATENTS said conveyor means in spaced relation to an image 2,820,716 1/1958 Hadmon et al. 1717.5 member moving through the machine, said roller 3,169,886 2/1965 Simm 118637 electrode having a multiplicity of electrically conductive spikes forming a multiplicity of corona discharge elements projecting outwardly from said RALPH G. NILSON, Primary Examiner.

WILLIAM F. LINDQUIST, Assistant Examiner. 

1. AN IMPROVED CHARGING MACHINE FOR XEROGRAPHIC, ELECTROPHOTOGRAPHIC, AND LIKE ELECTROSTATIC CHARGE IMAGE MEMBERS COMPRISING: A BASE; CONVEYOR MEANS, SUPPORTED ON SAID BASE, FOR RECEIVING AN IMAGE MEMBER TO BE CHARGED; MEANS TO DRIVE SAID CONVEYOR MEANS TO CARRY AN IMAGE MEMBER THROUGH THE MACHINE ALONG A GIVEN PATH; A ROLLER ELECTRODE, EXTENDING ACROSS ONE SIDE OF SAID CONVEYOR MEANS IN SPACED RELATION TO AN IMAGE MEMBER MOVING THROUGH THE MACHINE WITH THE AXIS OF SAID ROLLER ELECTRODE EXTENDING TRANSVERSELY TO SAID PATH, SAID ROLLER ELECTRODE HAVING A MULTIPLICITY ELECTRICALLY CONDUCTIVE SPIKES FORMING A MULTIPLICITY OF CORONA DISCHARGE ELEMENTS PROJECTING OUTWARDLY FROM SAID ROLLER IN STAGGERED ROWS AND ALL ELECTRICALLY CONNECTED TO EACH OTHER; MEANS FOR ROTATING SAID SPIKED ROLLER ELECTRODE AT A SPEED AND IN A DIRECTION SUCH THAT THERE IS A SUBSTANTIAL DIFFERENTIAL IN SPEED BETWEEN THE ENDS OF THE SPIKES AND THE IMAGE MEMBER AS THE IMAGE MEMBER IS FED THROUGH THE MACHINE PAST THE ROLLER ELECTRODE BY SAID CONVEYOR MEANS; A BASE ELECTRODE DISPOSED ON THE OPPOSITE SIDE OF SAID CONVEYOR MEANS FROM SAID ROLLER ELECTRODE AND FACING THE OPPOSITE SIDE OF THE IMAGE MEMBER FROM SAID ROLLER ELECTRODE; AND MEANS TO APPLY A UNIDIRECTIONAL ELECTRICAL POTENTIAL BETWEEN SAID ROLLER ELECTRODE AND SAID BASE ELECTRODE TO CAUSE A CORONA DISCHARGE BETWEEN SAID SPIKES AND SAID BASE ELECTRODE TO CHARGE THE IMAGE MEMBER. 